The objectives of this study are (1) to determine which preoperative risk factors are significantly related to the probability of a coronary artery bypass graft (CABG) patient experiencing an in-hospital mortality or perioperative complication, and (b) to use this information to assess the relative quality of care provided by hospitals and surgeons performing coronary artery bypass surgery. This work is an extension of a previous study conducted by the investigators in two respects: first, a new and substantially expanded data base will be used to identify potentially significant preoperative risk factors, and second, in addition to relating the preoperative risk factors to mortality, we will also relate them to perioperative complications. The specific aims of the study are as follows: (1) Develop a statistical model that describes the association between the probability of mortality for CABG patients and the expanded set of preoperative risk factors now available in the New York State cardiac surgery data base; (2) Determine which of the 30 New York State hospitals have significantly higher and lower mortality rates than expected given the preoperative severity of illness of their patients. Also, calculate the risk-adjusted (indirectly standardized) mortality rate for each hospital so hospitals can be compared with one another after having controlled for differences in severity of illness; (3) Develop a statistical model that describes the association between the probability of perioperative complications for CABG patients and the expanded set of perioperative risk factors. Determine whether any of the new risk factors are significantly related to the complications; (4) Determine which of the New York State hospitals have significantly higher and lower complication rates than expected given the preoperative severity of illness of their patients. Also, calculate the risk-adjusted complication rate for each hospital; and (5) Compare each hospital's risk-adjusted mortality rate and risk-adjusted complication rate to determine whether a strong relationship exists between the two performance measures. Also, compare the significant preoperative risk factors for mortality with the significant risk factors for complications, and determine whether hospitals with significantly higher (lower) mortality rates than expected also have significantly higher (lower) complications rates than expected.